This proposal concerns the genetic and molecular analysis of the temperature sensitive arrested development (ad4) mutants of the plant Arabidopsis thaliana. Homozygotes for the add1 mutation lose meristem organization at high temperature, while add3 homozygotes fail to complete a normal program of leaf formation. The add1 mutation was induced by a DNA mutagen and is therefore likely to be a knockout allele of the gene. Sequencing of the genomic region surrounding this genetic lesion and transformation rescue experiments have been performed to define the molecular extent of this gene. The pattern of ADD1 gene expression will also be assayed to determine if the gene functions specifically in the meristem, or acts in both leaves and the meristem. This will help determine if the impact of the add1 mutant on both leaves and meristems is a direct or indirect effect of the loss of normal ADD1 action. A high-resolution genetic map, using recombination breakpoints, has been generated to provide a precise location of the ADD3 locus on extant physical and sequence maps of the Arabidopsis genome. A bacterial artificial chromosome contig will be used to isolate sequence for the ADD3 gene. Transformation rescue experiments will be performed to verify the identity of this locus, and a candidate serine kinase will be sequenced to assess the likelihood that this gene is ADD3. Histological and morphological analysis will also be performed to characterize cell types missing or absent from upshifted add3 plants. Each mutation has some impact on both leaf and meristem function. Characterization of these genes is likely to shed more light on a poorly understood phenomenon, the regulatory cross-talk occurring between leaves and meristems throughout development.